This invention relates generally to turbines, and more specifically, to a nozzle box for increasing the efficiency of a flow directed to a turbine.
By way of a more detailed background, and with reference to FIG. 1, a control or first stage 10 of a conventional turbine includes a nozzle box 12 surrounding a rotor 14, the turbine control stage represented by a single bucket 16. Nozzle box 12 generally includes a torus portion 18, a bridge ring assembly 20 and a partition ring assembly 22. In turbines of this type, steam is fed into torus portion 18 of nozzle box 12, and is directed axially between outer bridge ring 24 and inner bridge ring 26, and between a plurality of circumferentially spaced bridge elements 28, which bridge elements 28 connect rings 24 and 26. The steam then flows through partition ring assembly 22 towards bucket(s) 16. Partition ring assembly typically comprises of radially inner and outer bands 30 and 32 (each formed in 180.degree. segments which, when the turbine is fully assembled, form 360.degree. rings), respectively, which hold between them a large number (for example, 100) of vane-shaped partition elements 34, which partition elements 34 serve to direct the steam at a desired angle to the bucket blades. Steampath assembly 22 is welded in place between upper and lower rings 24, 26 by circumferentially extending welds 36, 38. Rings 24, 26 are, in turn, welded to torus 18 by means of circumferential welds 40, 42. Nozzle box 12 is supported within a turbine inner shell 44 by a plurality of lugs 46 (one shown) welded to the outside of torus 18 and bridge ring assembly 20, in an area radially adjacent partition ring assembly 22. Nozzle box 12 is also keyed to inner shell 44 at 48.
Within conventional nozzle box designs, however, there exists significant circumferential variation in the cylindrical flow angle and a hub-strong velocity profile of the flow entering the first stage nozzle. This type of inlet distortion can lead to a significant loss in first stage efficiency.
Accordingly, there is a need in the art for an improved nozzle box.